The present invention relates to a fastener for insertion through aligned apertures in workpiece members thereby to secure the members together, and particularly for fasteners suitable for low grip applications, i.e. applications wherein the total width of the workpiece members being secured together is relatively small.
A currently known fastener for insertion through aligned apertures in workpiece members is commercially available under the Registered Trade Mark AVTAINER, as illustrated in FIGS. 1a to 3. The known fastener 2 comprises a pin 6 (as shown in FIG. 1a), and a body 4 (as shown in FIG. 1b). The pin comprises a shaft 42, a head 44, and a breakneck point 46. The body comprises a shell 8 and a nylon sleeve 10. The shell 8 comprises a radially enlarged head 12 at one end and an elongated shank 14 protruding therefrom, and a bore 16 extending axially completely through the body 4. The sleeve 10, which is located inside the elongated shank 14 of the shell 8, forms a first engaging means, and a barbed portion 52 comprising a plurality of annular barbs 18 on the pin 6 form a second engaging means.
FIGS. 2a and 2b illustrate the installation sequence of fastener 2 into a workpiece comprising workpiece members 20, 22. Firstly, as shown in FIG. 2a, the pin 6 is driven into the aligned apertures 54, 56 provided in the workpiece members 20, 22, by applying a force to the pin head 44. A plain portion 78 of the pin shank 42 is a press fit within the workpiece apertures 54, 56. FIG. 2a shows the pin 6 after it has been driven into the aligned apertures 54, 56.
Subsequently the body 4 is pushed, shank 14 first, onto the protruding end of the pin shank 42, until the leading end of the sleeve 10 abuts the barbed portion 52 of the pin 6. FIG. 2b shows the fastener after this stage has been completed.
The installation of the fastener 2 is completed by using a tool (not shown) to simultaneously pull the pin 42 shank and force the body 4 further along the pin shank 42 until the barbs 18 of the pin 6 mutually engage with the sleeve 10 of the body 4, and the underside surface 58 of the shell head 12 abuts the outer face 72 of workpiece member 22 remote from the pin head 44. The pin shank 142 is pulled until the it fails in tension at the breakneck point 46.
FIG. 3 shows the fastener 2 fully installed into the workpiece to secure workpiece members 20, 22 together, wherein the barbs 18 of the pin 6 are embedded into sleeve 10 of the body 4. The grip, i.e. the total thickness of the workpiece members 20, 22, is indicated by S. To provide the necessary tensile strength of the installed fastener 2, all barbs 18 must be engaged with the sleeve 10, and therefore the grip S must be greater than the length L of the shank 14, because the sleeve 10 is enclosed within this length, and this length must be less than the grip S to ensure that the joint is secured. Although the minimum grip could be reduced by reducing the length of the fastener 2, this would also result in an unacceptable reduction in tensile strength of the installed fastener. A reduction in the length over which the barbs 18 mutually engage with the sleeve 10 would result in an unacceptable reduction in the tensile strength of the installed fastener 2.
Accordingly, the minimum grip of the prior art fastener is restricted by the length of the shell, as the fastener cannot be used for grip values below the value of the shell length.
An aim of the present invention is to provide a fastener in which the minimum grip value is not limited by the length of the shell.
Accordingly the present invention provides, in a first aspect, a fastener comprising a pin and a body; the pin comprising a radially enlarged head at one end and an elongated shank protruding therefrom; the body comprising a shell having a radially and axially enlarged head at a head end and an elongated shank protruding therefrom, and wherein an underhead contact surface is provided on the shell head; and wherein a bore extends axially throughout the shell head and the shell shank; the body further comprising a first engaging means located within at least part of the bore and having a leading end and a trailing end, the leading end being further away from the head end of the shell than the trailing end; wherein a second engaging means is located on the exterior of at least part of the pin shank, wherein the pin shank is insertable into the bore of the body from an end of the body remote from the head end, such that the first and second engaging means mutually engage, wherein the underhead contact surface of the shell head is located at an axial level between the leading end and the trailing end of the first engaging means.
The head of the body may be formed of a radiused member, wherein underhead contact surface is provided on an annular flange of the radiused member.
The first engaging means preferably comprises a nylon sleeve, and the second engaging means preferably comprises a plurality of barbs.
The present invention provides, in a further aspect, a method of securing a workpiece together using a fastener comprising a pin and a body; the pin comprising a radially enlarged head at one end and an elongated shank protruding herefrom; the body comprising a shell having a radially and axially enlarged head at a head end and an elongated shank protruding therefrom, and wherein an underhead contact surface is provided on the shell head; and wherein a bore extends axially throughout the shell head and the shell shank; the body further comprising a first engaging means located within at least part of the bore and having a leading end and a trailing end, the leading end being further away from the head end of the shell than the trailing end; wherein a second engaging means is located on the exterior of at least part of the pin shank, wherein the pin shank is insertable into the bore of the body from an end of the body remote from the head end, such that the first and second engaging means mutually engage, wherein the underhead contact surface of the shell head is located at an axial level between the leading end and the trailing end of the first engaging means, wherein the workpiece comprises a first and a second workpiece member, which method comprises; inserting the pin of the fastener into aligned apertures in the first and second workpiece members until an underside surface of the pin head abuts an outer face of the first workpiece member and part of the pin shank protrudes from an outer face of the second workpiece member; subsequently, positioning the body of the fastener, shank first, over the protruding end of the pin shank, until the leading end of the first engaging means abuts the second engaging means; subsequently, applying pressure to the body thereby to push the body into the apertures of the first and second workpiece members, until the underhead contact surface contacts the outer face of the second workpiece member; and pulling the protruding end of the pin shank relative to the body, thereby causing the first engaging means and the second engaging means to mutually engage; wherein the protruding end of the pin shank is pulled relative to the body until the pin shank breaks at a breakneck point.